1. Field of the Invention
The present invention relates to optical waveguide elements and a process for producing the same. More particularly, the invention relates to optical waveguide elements which may be favorably used, for example, as curved optical waveguide elements for optical modulators, optical wavelength converters, optical splitters, optical switches, etc., as well as to the process for producing such optical waveguide elements.
2. Related Art Statement
Recently, optical waveguide elements have been used for optical modulators, optical wavelength converters, optical splitters, optical switches, etc.
Such an optical waveguide: element is formed by thermally diffusing a doping material into a base material to vary a refractive index thereof, for instance according to a titanium diffusion method.
FIGS. 1(a) and 1(b) are sectional views illustrating a method for producing an optical waveguide element by diffusing titanium into lithium niobate as generally used.
As shown in FIG. 1(a), after a waveguide pattern 2 made of a titanium is formed on a substrate having an electro-optic effect by vapor deposition, an optical waveguide 3 is formed as shown in FIG. 1(b) by thermally dispersing the above titanium into the substrate 1 through heating the substrate 1 up to a given temperature.
However, when the optical waveguide is formed in this way, it has a semi-elliptical sectional shape.
An actual optical fiber to be connected to such an optical waveguide element has a concentric sectional shape of a mode pattern with that of the optical waveguide element. Therefore, when an optical waveguide device is actually used in the state that the optical fiber is connected to the optical waveguide 3 having the semi-elliptical sectional shape as shown in FIG. 1(b), the coupling efficiency between the waveguide and the optical fiber decrease and the light transmission loss increases due to mode mismatching.
The optical waveguides formed according to the conventional producing processes are in contact with air or materials having refractive indexes lower than that of substrates such as quartz at upper faces thereof. Therefore, surface-polishing techniques yielding highly polished surfaces were required to reduce the scattering loss caused by the surface roughness of the substrate materials.
Attempts have been made to form curved optical waveguides as the above optical waveguides to improve integrality of the above optical devices (to decrease the length of the devices). However, if such an optical waveguide is formed as mentioned above according to the conventional titanium diffusion method, the vertical asymmetry of the mode of the light propagating inside the optical waveguide is large. Therefore, the curved excess loss increases, and the light transmission loss becomes extremely large, so that the optical device having fully high integrality cannot be formed.
Further, curved excess loss increases have a large dependency upon polarization of light owing to the above asymmetry. Since the dependency of this loss upon the polarization of light in the optical devices causes deviations in the device-insertion loss owing to deviations in the polarization of light of the incident light, it is desirable to reduce such dependency as much as possible.
The present invention relates to an optical waveguide element and a process for producing the same, which can reduce the light propagation loss and dependency of the light propagation loss upon polarization of light.
The present invention relates to the process for producing an optical waveguide element by thermally diffusing a metal element or a metallic compound into a substrate having a photoelectric effect, comprising the steps of: forming a waveguide pattern on the substrate, said waveguide pattern comprising the metal element or the metallic compound; forming a film on a main plane of the substrate and covering the entire waveguide pattern, the film having an electro-optic effect; and effecting the thermal diffusion of the metallic element and the metallic compound into the substrate.
The present invention also relates to the optical waveguide-buried type element, comprising a substrate having an optoelectrical effect, and an optical waveguide formed by thermally diffusing a metal element or a metal compound, wherein a diffused concentration of the metal element or the metal compound is substantially symmetrical in vertical directions within a section of the optical waveguide and also substantially symmetrical in lateral directions from a center of the section of the optical waveguide, and the diffused concentration of the metal or the metallic compound decreases radially outwardly from the diffusion source as viewed from the center of the section of the optical waveguide.
The present invention will be appreciated upon reading the following description of the invention :when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes may be made by the skilled person in the art to which the invention pertains.